Collaborative studies on oncogenes integrated into cellular and viral genomes are pursued by parallel in vivo and in vitro studies. Newborn mice inoculate with viral vectors containing the oncogene mac produced unique vascular tumors, whereas similar recombinants containing the genes dbl, transforming growth factor (TGF)-alpha and platelet-derived growth factor (PDGF) have been negative in similar experiments. Fibroblast cultures transfected with the oncogenes dbl, PDGF, basic fibroblast growth factor (bFGF) and acidic fibroblast growth factor (aFGF) were consistently sarcomagenic, whereas those containing TGF-alpha or epidermal growth factor receptor (EGFR) proved benign. In contrast, combined transfection with TGF-alpha and EGFR proved highly malignant in several cultures.